how to write your first linux device driver

how to write your first linux device driver

0. environment
-ubuntu 1804 64bit

1. apt-get install linux-headers-$(uname -r)

2. code hello.c

#include <linux/init.h>
#include <linux/module.h>
MODULE_LICENSE("Dual BSD/GPL");

static int hello_init(void)
{
printk(KERN_ALERT "Hello, solidmango\n");
return ;
}

static void hello_exit(void)
{
printk(KERN_ALERT "Goodbye, solidmango\n");
}

module_init(hello_init);
module_exit(hello_exit);

3. Makefile

# If KERNELRELEASE is defined, we've been invoked from the
# kernel build system and can use its language.
ifneq ($(KERNELRELEASE),)
obj-m := hello.o
# Otherwise we were called directly from the command
# line; invoke the kernel build system.
else
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
default:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
endif

4. sudo insmod hello.ko

5. sudo rmmod hello

6. view result

sm@ubuntu:~/dev$ cat /var/log/syslog|grep solidmango
Sep  :: ubuntu kernel: [ 3041.143749] Hello, solidmango
Sep  :: ubuntu kernel: [ 3068.192172] Goodbye, solidmango

7. sign your kernel module

/lib/modules/4.15./build/scripts/sign-file sha512 /lib/modules/4.15./build/certs/signing_key.pem /lib/modules/4.15./build/certs/signing_key.x509 hello.ko

signing_key.pem and signing_key.x509 files are generated when build the linux kernel

reference
https://wiki.gentoo.org/wiki/Signed_kernel_module_support#Enabling_module_signature_verification